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Validity of Mite Drop Test

I saw a post on a thread not long ago that said not to rely on the mite drop test to determine mite levels. That got me thinking (dangerous I know).

My problem (in my head) is this: Different bees show different levels of hygienic behavior. This level, as I understand it, can vary even from hive to hive. Let's say hive A has a high mite, on the verge of death mite load. Unfortunately, they show nearly no hygienic behavior. As a result, the sticky board only reveals a low mite load.

Let's say hive B has a low mite load. Hive B has extremely hygienic bees. They groom, they chew, they tie blocks to mite legs and sink them in the feeder...they're bad dudes. As a result, the sticky board reveals a low mite load.

The only universal solution that my inexperienced brain can think of is this: All hives will present an accurate mite drop because mites naturally fall off from time to time with or without grooming by the bees.

Is a mite drop test a risky thing to be doing? Or do mites fall off at a measurable rate regardless?

Re: Validity of Mite Drop Test

Mites, like everything else, get old and die. The other ones that end up on the drop board are immatures that didn't get old enough to live by the time the bee larva emerged.

Drop board data is open to interpretation, for example with seasonal influences (brood, no brood). But as a general rough guide they can be useful, every starting out beekeeper should use a drop board at least at first, just so they are aware of what is going on, and mite population changes etc.

If a hive has no hygienic, or other, mite control mechanisms, that may mean less mites may show on the board. But then the mite population would grow unchecked, so in time, more mites would show on the board.

Other thing with drop boards, mites can be on them, next day you look, they are gone. Could be ants, whatever. So a zero read is not necessarily zero.

Re: Validity of Mite Drop Test

Whatever manner you use to determine as best you can what your varroa infestation level is like you have to compare results over time. Take a number of samples and readings. Is Hive A showing more mites per sample than Hive B? Is the sample taken today higher than the one taken last month? Does the sample taken today show a number of mites which makes me think it's time to treat?

One sample doesn't tell you much until compared to other samples taken at the same time or compared to samples taken at this time last year. If I sample my hives, prefer the ether roll technique, and see 3 mites, then I am not worried about that hive. If I see 10plus, then it's time to think about treating. Unless honey is being produced.

Re: Validity of Mite Drop Test

>Data over time is important.

I agree. It also helps you see ups and downs. Typically on hot days numbers go up. Typically on colder days the numbers go down. Typically in the fall as brood volume decreases the numbers go up. Typically a large population of bees will have higher numbers than a smaller number of bees. Typically through the season (from spring to fall) the numbers climb. So looking at the trend is more informative than just a number on a given day in a given hive.

Re: Validity of Mite Drop Test

Re: Validity of Mite Drop Test

Originally Posted by Michael Bush

>Data over time is important.

I agree. It also helps you see ups and downs. Typically on hot days numbers go up. Typically on colder days the numbers go down. Typically in the fall as brood volume decreases the numbers go up. Typically a large population of bees will have higher numbers than a smaller number of bees. Typically through the season (from spring to fall) the numbers climb. So looking at the trend is more informative than just a number on a given day in a given hive.

Typically, to borrow Michael's word, the annual peak of the mite population in a hive of bees comes a little while after the annual peak bee population in a hive. Probably a brood cycle or two.

Oldtimer,
In the mites to bees ratio, I believe that the lowest number of mites to bees occurs a brood cycle after our queens start laying again here in the Northern Hemisphere. The annual brood break which occurs in Northern Parts of our country helps cut back on mite populations in hives.

As the life cycle of mites is dependent on the life cycle of bees, varroa laying their eggs in bee brrod cells, which you know, the expanding brood nest affords more brood for more varroa to reproduce in.

Someone more mathematical than I could illustrate this better than my words. But I believe you know basically how varroa reproduce, how many per cycle and such, so varroa to bee ratio should be pretty close to the highest counts soon here in the Northern Part of the Northern Hemisphere. Sept./Oct. I believe, as pretty soon we will probably see bee brood contraction occuring during the next cpl of months and on into the Fall and Winter,

Re: Validity of Mite Drop Test

> if the population increases through the season, that implies the other part of the season they come down. By what mechanism does this happen in a non treated hive?

I'd say it works out quite differently in small cell. With plenty of drone comb for the mites to reproduce in (and a slightly smaller cell for most drones leading to a slightly shorter cycle somewhat countering that) and less Varroa in the worker cells, the actual number probably goes up more in the spring than a large cell hive. When drone rearing falls off, there are more phoretic mites and less in cells, so the mite fall will probably increase. Mid summer is when I find the most mites. Then I would guess they are not reproducing well without the drone cells so the numbers continue to drop. By fall I have trouble finding any mites.

Re: Validity of Mite Drop Test

Interesting. Mike, Solomon did a post a while back with photos, where he pulled brood and counted mites. The infestation rate of the hive was drone brood 27%, worker brood 7%. This was the identical ratio one would typically find in a large cell hive, so it was an interesting thread.

Anyhow, I'm open to what both you and Mark said, long as it's consistent with real evidence.

Where I am, there is no winter brood break, they raise brood 365 days of the year. The mite population continues to grow through winter no different than summer.

Re: Validity of Mite Drop Test

Mites, like everything else, get old and die. The other ones that end up on the drop board are immatures that didn't get old enough to live by the time the bee larva emerged.

If a hive has no hygienic, or other, mite control mechanisms, that may mean less mites may show on the board. But then the mite population would grow unchecked, so in time, more mites would show on the board.

Other thing with drop boards, mites can be on them, next day you look, they are gone. Could be ants, whatever. So a zero read is not necessarily zero.

This was the explanation I was looking for. I didn't even consider the mites that naturally die.

Re: Validity of Mite Drop Test

Well i'm going through that right now . I have been fogging all year this year with FGMO and things where going good 5 mite in 24 hours and lower then about 2 weeks ago I started to get 10 to 20 so a did alcohol washes on my hives and they looked good but I put the wrong amount of bees in the jars and used the wrong size jars . So then I got the right size jars and use the right amount of bees and things changed all hives need treated by alcohol wash standards . So now I have oxalic acid vaporizer and I have done 4 hives and that was Wed. so the sticky boards are littered with mites and the mites look {darker} different then what was dropping with fogging .
Mite drop test have got me crazy but I think the oxalic acid is working . I am going to do the oxalic acid treatment for 3 weeks and then do alcohol washes I bet the counts are low.

Re: Validity of Mite Drop Test

Sounds like a plan, but with the OA vapour weekly for 3 weeks, there's always a few mites slip through. If you could follow that with one more OA treatment when the bees go broodless in winter (but before they have tightly clustered), you should be sweet.